A custom ListView for Xamarin.Android that enables scrolling via moving a DragShadow to the top or bottom.

XamarinScrollableListView.cs

// File: XamarinScrollableListView.cs
// Created: 27.07.2016
//
// This class represents a custom View. It inherits from ListView but adds automatic Drag and Drop scrolling.

using Android.Content;
using Android.Runtime;
using Android.Util;
using Android.Views;
using Android.Widget;
using Java.Lang;

namespace yournamespace
{
    [Register("your.package.name.here.yournamespace.XamarinScrollableListView")]
    public sealed class XamarinScrollableListView : ListView
    {
        private bool isScrolling;
        private float lastY;
        private int scrollBy;

        public XamarinScrollableListView(Context context, IAttributeSet attrs) : base(context, attrs)
        {
            this.Drag += this.OnDrag;
            this.SetOnScrollListener(new OnScrollListener(this));
        }

        private void OnDrag(object sender, DragEventArgs args)
        {
            if (args.Event.Action == DragAction.Location)
            {
                this.lastY = args.Event.GetY();
                this.ScrollUpdate(this.lastY);
            }
            else if (args.Event.Action == DragAction.Ended)
            {
                this.isScrolling = false;
            }
        }

        private void ScrollUpdate(float y)
        {
            var height = this.Height;
            var scrollBorder = height/3;
            var position = (int) y;

            this.scrollBy = 0;

            if (position < scrollBorder)
            {
                this.scrollBy = -(scrollBorder - position);
            }
            else if (position > height - scrollBorder)
            {
                this.scrollBy = position - (height - scrollBorder);
            }

            if (this.scrollBy == 0)
            {
                this.isScrolling = false;
                return;
            }

            // Math incoming: A quadratic function with some division eases to smooth out scroll speed
            this.scrollBy = (int) (Math.Pow(this.scrollBy/7d, 2)/(scrollBorder/10d))*(this.scrollBy < 0 ? -1 : 1);

            if (this.isScrolling)
            {
                this.SmoothScrollBy(this.scrollBy, 0);
            }
            this.isScrolling = true;
        }

        private class OnScrollListener : Object, IOnScrollListener
        {
            private readonly XamarinScrollableListView super;
            private int prevFirstVisibleItem;
            private int prevLastVisibleItem;

            public OnScrollListener(XamarinScrollableListView super)
            {
                this.super = super;
            }

            public void OnScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount)
            {
                var lastVisibleItem = firstVisibleItem + visibleItemCount - 1;

                View child = null;
                if (firstVisibleItem != this.prevFirstVisibleItem)
                {
                    child = this.super.GetChildAt(0);
                }

                if (this.prevLastVisibleItem != lastVisibleItem)
                {
                    child = this.super.GetChildAt(this.super.ChildCount - 1);
                }

                if (child != null)
                {
                    // Workaround to set newly scrolled items as valid drop targets
                    child.Visibility = ViewStates.Invisible;
                    child.Visibility = ViewStates.Visible;
                }

                this.prevLastVisibleItem = lastVisibleItem;
                this.prevFirstVisibleItem = firstVisibleItem;
            }

            public void OnScrollStateChanged(AbsListView view, ScrollState scrollState)
            {
                if (this.super.isScrolling)
                {
                    this.super.SmoothScrollBy(this.super.scrollBy, 0);
                }
            }
        }
    }
}